Laser device

ABSTRACT

A laser device may include: a master oscillator including a first laser chamber, a first pair of discharge electrodes provided in the first laser chamber, and an optical resonator, the master oscillator being configured to output a laser beam; a first amplifier including a second laser chamber provided in an optical path of the laser beam outputted from the master oscillator and a second pair of discharge electrodes provided in the second laser chamber at a first gap distance, the first amplifier being configured to amplify the laser beam; and a first beam-adjusting optical system provided in an optical path of the laser beam between the master oscillator and the first amplifier, the first beam-adjusting optical system being configured to adjust the laser beam outputted from the master oscillator such that a beam width of the laser beam entering the first amplifier measured in a direction of electric discharge between the second pair of discharge electrodes is substantially equal to the first gap distance between the second pair of discharge electrodes.

TECHNICAL FIELD

The present disclosure relates to a laser device.

BACKGROUND ART

A laser annealing apparatus may apply a pulsed laser beam on anamorphous silicon film formed on a substrate. The pulsed laser beam maybe emitted from a laser system such as an excimer laser system. Thepulsed laser beam may have a wavelength of ultraviolet light region.Such pulsed laser beam may reform the amorphous silicon film to apoly-silicon film. The poly-silicon film can be used to form thin filmtransistors (TFTs). The TFTs may be used in large-sized liquid crystaldisplays.

Patent Document 1

Japanese Patent Application Publication No. 2009-277977 A

Patent Document 2

U.S. Pat. No. 8,803,027 B

Patent Document 3

Japanese Patent No. 4818871 B

Patent Document 4

Japanese Patent No. 5376908 B

SUMMARY

A laser device according to an aspect of the present disclosure mayinclude: a master oscillator including a first laser chamber, a firstpair of discharge electrodes provided in the first laser chamber, and anoptical resonator, the master oscillator being configured to output alaser beam; a first amplifier including a second laser chamber providedin an optical path of the laser beam outputted from the masteroscillator and a second pair of discharge electrodes provided in thesecond laser chamber at a first gap distance, the first amplifier beingconfigured to amplify the laser beam; and a first beam-adjusting opticalsystem provided in an optical path of the laser beam between the masteroscillator and the first amplifier, the first beam-adjusting opticalsystem being configured to adjust the laser beam outputted from themaster oscillator such that a beam width of the laser beam entering thefirst amplifier measured in a direction of electric discharge betweenthe second pair of discharge electrodes is substantially equal to thefirst gap distance between the second pair of discharge electrodes.

A laser device according to another aspect of the present disclosure mayinclude: a master oscillator including a first laser chamber, a firstpair of discharge electrodes provided in the first laser chamber, and anoptical resonator, the master oscillator being configured to output alaser beam; a first amplifier including a second laser chamber providedin an optical path of the laser beam outputted from the masteroscillator and a second pair of discharge electrodes provided in thesecond laser chamber, the first amplifier being configured to amplifythe laser beam; and a first beam-adjusting optical system provided in anoptical path of the laser beam between the master oscillator and thefirst amplifier, the first beam-adjusting optical system beingconfigured to adjust the laser beam outputted from the masteroscillator, the first beam-adjusting optical system including a firstoptical element with a positive power and a second optical element witha positive or negative power provided downstream from the first opticalelement in the optical path of the laser beam.

A laser device according to another aspect of the present disclosure mayinclude: a master oscillator including a first laser chamber, a firstpair of discharge electrodes provided in the first laser chamber, and anoptical resonator, the master oscillator being configured to output alaser beam; a first amplifier including a second laser chamber providedin an optical path of the laser beam outputted from the masteroscillator and a second pair of discharge electrodes provided in thesecond laser chamber, the first amplifier being configured to amplifythe laser beam; and a first beam-adjusting optical system provided in anoptical path of the laser beam between the master oscillator and thefirst amplifier, the first beam-adjusting optical system being aboth-side telecentric optical system.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary embodiments of the present disclosure will be described belowas mere examples with reference to the appended drawings.

FIG. 1A schematically shows a configuration of a laser device accordingto a comparative example.

FIG. 1B shows a power amplifier PA shown in FIG. 1A as viewed in adirection parallel to a direction of electric discharge between a pairof discharge electrodes.

FIG. 2A shows a beam profile in a cross section of a beam at line IIA inFIG. 1A.

FIG. 2B shows a beam profile in a cross section of the beam at line IIBin FIG. 1A.

FIG. 2C shows a beam profile in a cross section of the beam at line IICin FIG. 1A.

FIG. 3A schematically shows a configuration of a laser device accordingto a first embodiment of the present disclosure.

FIG. 3B schematically shows the configuration of the laser deviceaccording to the first embodiment of the present disclosure.

FIG. 4A shows a beam profile in a cross section of a beam at line IVA inFIG. 3A.

FIG. 4B shows a beam profile in a cross section of the beam at line IVBin FIG. 3A.

FIG. 4C shows a beam profile in a crass section of the beam at line IVCin FIG. 3A.

FIG. 5A shows a beam-adjusting optical system 40 a as viewed in a −Vdirection as a first example of a beam-adjusting optical system shown inFIG. 3A.

FIG. 5B shows the beam-adjusting optical system 40 a as viewed in a −Hdirection.

FIG. 6A shows a beam-adjusting optical system 40 b as viewed in the −Vdirection as a second example of the beam-adjusting optical system shownin FIG. 3A.

FIG. 6B shows the beam-adjusting optical system 40 b as viewed in the −Hdirection.

FIG. 7A shows a beam-adjusting optical system 40 c as viewed in the −Vdirection as a third example of the beam-adjusting optical system shownin FIG. 3A.

FIG. 7B shows the beam-adjusting optical system 40 c as viewed in the −Hdirection.

FIG. 8A shows a beam-adjusting optical system 40 d as viewed in the −Vdirection as a fourth example of the beam-adjusting optical system shownin FIG. 3A.

FIG. 8B shows the beam-adjusting optical system 40 d as viewed in the −Hdirection.

FIG. 9A shows a beam-adjusting optical system 40 e as viewed in the −Vdirection as a fifth example of the beam-adjusting optical system shownin FIG. 3A.

FIG. 9B shows the beam-adjusting optical system 40 e as viewed in the −Hdirection.

FIG. 10A schematically shows a configuration of a laser device accordingto a second embodiment of the present disclosure.

FIG. 10B schematically shows the configuration of the laser deviceaccording to the second embodiment of the present disclosure.

FIG. 11A shows a beam profile in a cross section of a beam at line XIAin FIG. 10A.

FIG. 11B shows a beam profile in a cross section of the beam at line XIBin FIG. 10A.

FIG. 11C shows a beam profile in a cross section of the beam at line XICin FIG. 10A.

FIG. 12A schematically shows a configuration of a laser device of amodified example according to the second embodiment of the presentdisclosure.

FIG. 12B schematically shows the configuration of the laser device ofthe modified example according to the second embodiment of the presentdisclosure.

FIG. 13 schematically shows a configuration of a laser device accordingto a third embodiment of the present disclosure.

FIG. 14A schematically shows an optical arrangement of the laser deviceshown in FIG. 13.

FIG. 14B schematically shows an optical arrangement of a laser device ofa first modified example according to the third embodiment of thepresent disclosure.

FIG. 14C schematically shows an optical arrangement of a laser device ofa second modified example according to the third embodiment of thepresent disclosure.

DESCRIPTION OF EMBODIMENTS

Contents

-   1. Outline-   2. Laser Device According to Comparative Example    -   2.1 Configuration of MOPA Laser    -   2.2 Operation of MOPA Laser    -   2.3 Problem-   3. Laser Device Including Beam-Adjusting Optical System    -   3.1 Configuration    -   3.2 Operation    -   3.3 Effect    -   3.4 Others    -   3.5 First Example of Beam-Adjusting Optical System    -   3.6 Second Example of Beam-Adjusting Optical System    -   3.7 Third Example of Beam-Adjusting Optical System    -   3.8 Fourth Example of Beam-Adjusting Optical System    -   3.9 Fifth Example of Beam-Adjusting Optical System-   4. Laser Device Including Both-Side Telecentric Beam-Adjusting    Optical System    -   4.1 Configuration    -   4.2 Operation    -   4.3 Effect    -   4.4 Others    -   4.5 Modified Example of Second Embodiment-   5. Laser Device Including Plurality of Power Amplifiers    -   5.1 Configuration    -   5.2 Operation and Effect    -   5.3 Modified Examples of Third Embodiment

Embodiments of the present disclosure will be described below in detailwith reference to the drawings. The embodiments described below mayrepresent several examples of the present disclosure and may not intendto limit the content of the present disclosure. Not all of theconfigurations and operations described in the embodiments areindispensable in the present disclosure. Identical reference symbols maybe assigned to identical elements and redundant descriptions may beomitted.

1. OUTLINE

A laser annealing apparatus may perform laser annealing by irradiatingan amorphous silicon film on a glass substrate with a pulsed laser beamat a predetermined energy density. The pulsed laser beam may be demandedto increase its energy per one pulse for enlarging irradiation area atthe predetermined energy density to manufacture larger and larger liquidcrystal displays as in recent years. Increasing energy per one pulse maybe achieved by using two-chamber system including a master oscillator(MO) and a power amplifier (PA). Such laser device using the two-chambersystem may be referred to as a MAPA laser.

The laser beam outputted from the master oscillator may have a positivedivergence and thus the diameter of the beam may increase before thebeam enters the power amplifier. If the diameter of the beam exceeds adimension of a discharge space of the power amplifier, a part of thelaser beam that does not enter the discharge space of the poweramplifier may be wasted. This may cause reduction of efficiency of laserbeam generation with the MOPA laser. Such problem may occur if, forexample, a discharge space of the master oscillator and a dischargespace of the power amplifier is substantially the same in size and themaster oscillator and the power amplifier are distanced from each other.

According to one aspect of the present disclosure, a firstbeam-adjusting optical system provided in an optical path between themaster oscillator and the power amplifier may include a first opticalelement with a positive power and a second optical element with apositive or negative power disposed downstream from the first opticalelement in the optical path of the laser beam.

According to another aspect of the present disclosure, the firstbeam-adjusting optical system provided in the optical path between themaster oscillator and the power amplifier may be a both-side telecentricoptical system.

The first beam-adjusting optical system may adjust the laser beam suchthat a beam width of the laser beam entering the power amplifier issubstantially equal to a gap distance between a pair of dischargeelectrodes of the power amplifier.

2. LASER DEVICE ACCORDING TO COMPARATIVE EXAMPLE 2.1 CONFIGURATION OFMOPA LASER

FIG. 1A schematically shows a configuration of a laser device accordingto a comparative example. This laser device may be a MOPA laserincluding a master oscillator MO, a power amplifier PA, and a pluralityof high-reflective mirrors 18 and 19. FIG. 1A shows a view in adirection perpendicular to a direction of travel of the laser beam andperpendicular to a direction of electric discharge between a pair ofdischarge electrodes in the master oscillator MO and that in the poweramplifier PA. FIG. 1B shows the power amplifier PA shown in FIG. 1A asviewed in a direction parallel to the direction of electric dischargebetween the pair of discharge electrodes in the power amplifier PA. Thedirection of travel of the laser beam may be a Z direction. Thedirection of electric discharge between the pair of discharge electrodesof the master oscillator MO or that in the power amplifier PA may be a Vdirection. The direction perpendicular to both of the Z direction andthe V direction may be an H direction. As the direction of travel ischanged by the high-reflective mirror 18 or 19 reflecting the laserbeam, the Z direction and the V direction may be changed.

The master oscillator MO may include a first laser chamber 10, a firstpair of discharge electrodes 11 a and 11 b, a rear mirror 14, and anoutput coupling mirror 15. The first pair of discharge electrodes 11 aand 11 b may be provided in the first laser chamber 10. The rear mirror14 and the output coupling mirror 15 may constitute an opticalresonator. A discharge space between the first pair of dischargeelectrodes 11 a and 11 b may be located between the rear mirror 14 andthe output coupling mirror 15. The rear mirror 14 may be a mirror toreflect the laser beam at a high reflectance. The output coupling mirror15 may be made of a substrate such as CaF₂ crystal to transmit anexcimer laser beam and may be coated with a partially-reflective film toreflect the excimer laser beam at a rate in a range from 10% to 40%. Thefirst laser chamber 10 may have windows 10 a and 10 b at respective endsof the first laser chamber 10.

The high-reflective mirrors 18 and 19 may be disposed such that thepulsed laser beam outputted from the master oscillator MO enters thepower amplifier PA as a seed beam.

The power amplifier PA may include a second laser chamber 20 and asecond pair of discharge electrodes 21 a and 21 b. The second pair ofdischarge electrodes 21 a and 21 b may be provided in the second laserchamber 20. The second laser chamber 20 may have windows 20 a and 20 bat respective ends of the second laser chamber 20.

The first laser chamber 10 and the second laser chamber 20 may eachstore excimer laser gas. The excimer laser gas may include a rare gassuch as argon gas, krypton gas or xenon gas, a halogen gas such asfluorine gas or chlorine gas, and a buffer gas such as neon gas orhelium gas.

The discharge space between the first pair of discharge electrodes 11 aand 11 b and the discharge space between the second pair of dischargeelectrodes 21 a and 21 b may have substantially the same forms and sizeswith each other. A gap distance between the first pair of dischargeelectrodes 11 a and 11 b and a gap distance between the second pair ofdischarge electrodes 21 a and 21 b may thus be substantially equal toeach other.

The windows 10 a, 10 b, 20 a and 20 b may each be made of CaF₂ crystalor the like to transmit the excimer laser beam. The windows 10 a, 10 b,20 a and 20 b may each be inclined in the H direction at a Brewster'sangle to suppress reflection of the laser beam.

2.2 OPERATION OF MOPA LASER

FIG. 2A shows a beam profile in a cross section of the laser beam atline IIA in FIG. 1A. FIG. 2B shows a beam profile in a cross section ofthe laser beam at line IIB in FIG. 1A. FIG. 2C shows a beam profile in across section of the laser beam at line IIC in FIG. 1A.

A power source (not shown) in the master oscillator MO may apply apulsed high voltage to the first pair of discharge electrodes 11 a and11 b. The pulsed high voltage applied to the first pair of dischargeelectrodes 11 a and 11 b may cause pulsed electric discharge between thefirst pair of discharge electrodes 11 a and 11 b. The laser gas may beexcited by energy of the electric discharge and may shift to a highenergy level. The excited laser gas may then shift back to a low energylevel to emit light having a certain wavelength depending on thedifference between the energy levels. In the excimer laser device, thislight may include ultra-violet rays. The light generated in the firstlaser chamber 10 may be emitted from the first laser chamber 10 throughthe windows 10 a and 10 b. The light may travel back and forth betweenthe rear mirror 14 and the output coupling mirror 15 constituting theoptical resonator to form a standing wave. The light may reciprocatethrough the discharge space between the first pair of dischargeelectrodes 11 a and 11 b and thus be amplified, which causes laseroscillation.

The output coupling mirror 15 may transmit a part of the light generatedin the optical resonator. The master oscillator MO may thus output thepulsed laser beam. Here, the beam profile of the output laser beam mayhave a form as shown in FIG. 2A. The beam profile may have substantiallythe same size as the size of a cross section of the discharge spacebetween the first pair of discharge electrodes 11 a and 11 b.

As shown in FIG. 2A, the cross section of the laser beam outputted fromthe master oscillator MO may have a form relatively long in thedirection of electric discharge, namely, in the V direction. The crosssection of the laser beam may have a substantially rectangular form.Further, the beam profile in the V direction of the laser beam outputtedfrom the master oscillator MO may have a substantially top-hatdistribution having a substantially uniform energy density. Further, thebeam profile in the H direction of the laser beam outputted from themaster oscillator MO may have a Gaussian distribution having a highenergy density around the center of the distribution and having a lowenergy density around each end of the distribution.

The laser beam, diverging in respective angles of divergence in the Hdirection and the V direction, may be reflected by the high-reflectivemirrors 18 and 19 and then enter the window 20 a of the power amplifierPA as the seed beam. The beam profile of the pulsed laser beam enteringthe window 20 a may have a form as shown in FIG. 2B. A part of the laserbeam having entered the window 20 a may then enter the discharge spacebetween the second pair of discharge electrodes 21 a and 21 b. However,another part of the laser beam having entered the window 20 a maydeviate from the discharge space in ±V directions and hit the secondpair of discharge electrodes 21 a and 21 b, without entering thedischarge space. Further, still another part of the laser beam havingentered the window 20 a may deviate from the discharge space in ±Hdirections without entering the discharge space.

A pulsed high voltage may be applied to the second pair of dischargeelectrodes 21 a and 21 b by a power source (not shown) insynchronization with the part of the pulsed laser beam entering thedischarge space between the second pair of discharge electrodes 21 a and21 b. The pulsed high voltage applied to the second pair of dischargeelectrodes 21 a and 21 b may cause pulsed electric discharge between thesecond pair of discharge electrodes 21 a and 21 b. The laser gas may beexcited due to the electric discharge in the laser gas. As a result, thelaser beam passing through the gap between the second pair of dischargeelectrodes 21 a and 21 b may be amplified. The laser beam thus amplifiedmay be outputted from the power amplifier PA through the window 20 b.The beam profile of the pulsed laser beam outputted from the poweramplifier PA may have a form as shown in FIG. 2C. The laser beamoutputted through the window 20 b may gradually diverge. A beam width inthe V direction at the line IIC in FIG. 1A may thus be slightly largerthan the gap distance between the second pair of discharge electrodes 21a and 21 b.

2.3 PROBLEM

If the distance between the master oscillator MO and the power amplifierPA is large, the beam size of the laser beam entering the window 20 a ofthe power amplifier PA may be larger than the size of the cross sectionof the discharge space of the power amplifier PA. In that case, a partof the laser beam may fail to enter the discharge space of the poweramplifier PA and fail to be amplified. This may cause reduction ofefficiency of laser beam generation with the MOPA laser.

Embodiments according to the present disclosure are thus explainedbelow.

3. LASER DEVICE INCLUDING BEAM-ADJUSTING OPTICAL SYSTEM 3.1CONFIGURATION

FIGS. 3A and 3B schematically show a configuration of a laser deviceaccording to a first embodiment of the present disclosure. The laserdevice of the first embodiment may include a beam-adjusting opticalsystem 40 in the optical path of the laser beam between thehigh-reflective mirrors 18 and 19.

The beam-adjusting optical system 40 may be configured to adjust thebeam width in the V direction of the laser beam entering the poweramplifier PA to be substantially equal to the gap distance between thesecond pair of discharge electrodes 21 a and 21 b. The beam-adjustingoptical system 40 may include, for example, a cylindrical convex lens 41and a cylindrical concave lens 42.

3.2 OPERATION

FIG. 4A shows a beam profile in a crass section of the laser beam atline IVA in FIG. 3A. FIG. 4B shows a beam profile in a cross section ofthe laser beam at line IVB in FIG. 3A. FIG. 4C shows a beam profile in across section of the laser beam at line IVC in FIG. 3A.

The laser beam outputted from the master oscillator MO may be reflectedby the high-reflective mirror 16, and then enter the beam-adjustingoptical system 40. The beam-adjusting optical system 40 may convert thebeam profile of the laser beam such that the beam width in the Vdirection of the laser beam is substantially equal to the gap distancebetween the second pair of discharge electrodes 21 a and 21 b (see FIG.4B).

The laser beam, converted such that the beam width in the V direction issubstantially equal to the gap distance between the second pair ofdischarge electrodes 21 a and 21 b, may enter the discharge spacebetween the second pair of discharge electrodes 21 a and 21 b.

3.3 EFFECT

The configuration explained above, as compared to the configurationwithout the beam-adjusting optical system 40, may suppress the problemwhere a part of the laser beam hits the second pair of dischargeelectrodes 21 a and 21 b and is wasted. The pulse energy of the pulsedlaser beam outputted from the power amplifier PA may thus increase.

In the case where a part of the laser beam deviates in the ±H directionsas shown in FIG. 4B, the part of the laser beam at each of the sides inthe ±H directions may be wasted. However, the part of the laser beam ateach of the sides in the ±H directions may have a relatively low lightintensity. Therefore, energy to be wasted may not be so high.

3.4 OTHERS

The present embodiment shows an example where the beam-adjusting opticalsystem 40 is provided in the optical path between the high-reflectivemirrors 18 and 19. However, the present disclosure may not necessarilybe limited to this example. At least a part of the beam-adjustingoptical system 40 may be provided in the optical path between the outputcoupling mirror 15 and the high-reflective mirror 18 or the optical pathbetween the high-reflective mirror 19 and the window 20 a.

Further, the embodiment shows an example of the beam-adjusting opticalsystem that functions to adjust the beam width in the V direction to besubstantially equal to the gap distance between the second pair ofdischarge electrodes. However, the present disclosure may notnecessarily be limited to adjusting the beam width in the V direction.As explained below with reference to FIGS. 6A, 6B, 7A, 7B, 8A, and 8B,the beam width in the H direction may also be adjusted substantially tothe width of the discharge space in the H direction of the poweramplifier PA.

3.5 FIRST EXAMPLE OF BEAM-ADJUSTING OPTICAL SYSTEM

FIG. 5A shows a beam-adjusting optical system 40 a as viewed in the −Vdirection. The beam-adjusting optical system 40 a may represent a firstexample of the beam-adjusting optical system 40 according to the firstembodiment shown in FIG. 3A. FIG. 5B shows the beam-adjusting opticalsystem 40 a as viewed in the −H direction.

The beam-adjusting optical system 40 a may include a cylindrical convexlens 41 and a cylindrical concave lens 42. The cylindrical convex lens41 and the cylindrical concave lens 42 may be provided in an opticalpath of the laser beam. The cylindrical convex lens 41 may be locatedupstream from the cylindrical concave lens 42 in the optical path of thelaser beam.

The cylindrical convex lens 41 may have a rear-side focal axis F1located downstream from the cylindrical convex lens 41 in the opticalpath of the laser beam at a distance corresponding to a focal lengthFL1. When parallel rays of light are transmitted by the cylindricalconvex lens 41 from the left side in the figure, the rear-side focalaxis F1 of the cylindrical convex lens 41 may be an axis correspondingto a line focus on which the rays of light are to be focused at theright side. An optical element such as the cylindrical convex lens 41 bywhich parallel rays of light are transmitted and focused or an opticalelement such as a concave mirror by which parallel rays of light arereflected and focused may be referred to as an optical element with apositive power.

The cylindrical concave lens 42 may have a front-side focal axis F2located downstream from the cylindrical concave lens 42 in the opticalpath of the laser beam at a distance corresponding to a focal lengthFL2. When parallel rays of light are transmitted by the cylindricalconcave lens 42 from the right side in the figure, the rays of light maydiverge to the left side. The front-side focal axis F2 of thecylindrical concave lens 42 may be an axis corresponding to a line focuson which imaginary lines corresponding to the rays of light diverging tothe left side are to cross each other at the right side. An opticalelement such as the cylindrical concave lens 42 by which parallel raysof light are transmitted and made diverge or an optical element such asa convex mirror by which parallel rays of light are reflected and madediverge may be referred to as an optical element with a negative power.

The focal length FL2 of the cylindrical concave lens 42 may be shorterthan the focal length FL1 of the cylindrical convex lens 41. Therear-side focal axis F1 of the cylindrical convex lens 41 and thefront-side focal axis F2 of the cylindrical concave lens 42 may each besubstantially parallel to the H direction. The rear-side focal axis F1of the cylindrical convex lens 41 and the front-side focal axis F2 ofthe cylindrical concave lens 42 may be located in the vicinity of eachother. The front-side focal axis F2 of the cylindrical concave lens 42may be located slightly downstream from the rear-side focal axis F1 ofthe cylindrical convex lens 41 in the optical path of the laser beam.

The cylindrical convex lens 41 may be held by a holder 51. Thecylindrical concave lens 42 may be held by a holder 52. The holder 52,which holds the cylindrical concave lens 42, may be held by a uniaxialstage 53 and capable of moving along the optical path axis of the laserbeam. The holder 51 and the uniaxial stage 53 may be held by a plate 54.This may allow the cylindrical concave lens 42 to move in a directionparallel to the Z direction along the optical path axis of the laserbeam and to change distance from the cylindrical convex lens 41.

The uniaxial stage 53 may have a micrometer (not shown) to adjust thedistance between the cylindrical convex lens 41 and the cylindricalconcave lens 42 along the optical path axis of the laser beam. Themicrometer may move the cylindrical concave lens 42 such that the beamwidth in the V direction of the laser beam becomes substantially equalto the gap distance between the second pair of discharge electrodes 21 aand 21 b. The micrometer may be a manually operated micrometer or anautomatic micrometer. The automatic micrometer may be driven by acontroller (not shown).

The pulsed laser beam outputted from the master oscillator MO, which maybe a diverging beam gradually expanding its beam width, may be reflectedby the high-reflective mirror 18 and may enter the cylindrical convexlens 41 of the beam-adjusting optical system 40 a.

The laser beam incident on the cylindrical convex lens 41 as a divergingbeam may be changed to a converging beam by the cylindrical convex lens41. The converging beam gradually narrowing its beam width in the Vdirection may enter the cylindrical concave lens 42.

The front-side focal axis F2 of the cylindrical concave lens 42 may belocated slightly downstream from the rear-side focal axis F1 of thecylindrical convex lens 41 in the optical path of the laser beam. Inthis configuration, the laser beam transmitted by the cylindricalconcave lens 42 may be a nearly parallel beam.

The laser beam transmitted by the cylindrical concave lens 42 may becomea laser beam having a beam width in the V direction substantially equalto the gap distance between the second pair of discharge electrodes 21 aand 21 b and then enter the power amplifier PA.

As shown in FIG. 5B, let A be the beam width in the V direction of thelaser beam incident on the cylindrical convex lens 41 and let B be thebeam width in the V direction of the laser beam transmitted by thecylindrical concave lens 42. It is preferable that the followingformulae are satisfied:

B≈G, and

B/A≈FL2/FL1.

Here, G may be the gap distance between the second pair of dischargeelectrodes 21 a and 21 b. Based on the beam width A in the V directionof the laser beam incident on the cylindrical convex lens 41 and the gapdistance G between the second pair of discharge electrodes 21 a and 21b, the ratio FL2/FL1 of the focal lengths of the lenses may bedetermined and the beam width of the laser beam may be adjusted to adesirable value.

In this example, the rear-side focal axis F1 of the cylindrical convexlens 41 and the front-side focal axis F2 of the cylindrical concave lens42 may each be substantially parallel to the H direction. However, thepresent disclosure may not necessarily be limited to this example.

For another example, the rear-side focal axis F1 of the cylindricalconvex lens 41 and the front-side focal axis F2 of the cylindricalconcave lens 42 may be arranged substantially parallel to the Vdirection. In that case, the distance between the cylindrical convexlens 41 and the cylindrical concave lens 42 may be adjusted such thatthe beam width in the H direction of the laser beam becomessubstantially equal to the width of the discharge space of the poweramplifier PA.

3.6 SECOND EXAMPLE OF BEAM-ADJUSTING OPTICAL SYSTEM

FIG. 6A shows a beam-adjusting optical system 40 b as viewed in the −Vdirection. The beam-adjusting optical system 40 b may represent a secondexample of the beam-adjusting optical system 40 according to the firstembodiment shown in FIG. 3A. FIG. 6B shows the beam-adjusting opticalsystem 40 b as viewed in the −H direction.

The beam-adjusting optical system 40 b may be different from thebeam-adjusting optical system 40 a described with reference to FIGS. 5Aand 5B in that the cylindrical convex lens 41 is substituted by aspherical convex lens 45. Also, in the beam-adjusting optical system 40b, the cylindrical concave lens 42 may be substituted by a sphericalconcave lens 46.

The spherical convex lens 45 may have a rear-side focal point F1 locateddownstream from the spherical convex lens 45 in the optical path of thelaser beam at a distance corresponding to a focal length FL1. Whenparallel rays of light are transmitted by the spherical convex lens 45from the left side in the figure, the rear-side focal point F1 of thespherical convex lens 45 may be a point on which the rays of light areto be focused at the right side.

The spherical concave lens 46 may have a front-side focal point F2located downstream from the spherical concave lens 46 in the opticalpath of the laser beam at a distance corresponding to a focal lengthFL2. When parallel rays of light are transmitted by the sphericalconcave lens 46 from the right side in the figure, the rays of light maydiverge to the left side. The front-side focal point F2 of the sphericalconcave lens 46 may be a point on which imaginary lines corresponding tothe rays of light diverging to the left side are to cross each other atthe right side.

The rear-side focal point F1 of the spherical convex lens 45 and thefront-side focal point F2 of the spherical concave lens 46 may belocated in the vicinity of each other. The front-side focal point F2 ofthe spherical concave lens 46 may be located slightly downstream fromthe rear-side focal point F1 of the spherical convex lens 45 in theoptical path of the laser beam.

The spherical convex lens 45 may be held by a holder 51. The sphericalconcave lens 46 may be held by a holder 52.

The configuration of holding the lenses and adjusting their positionsmay be substantially the same as that of the first example describedwith reference to FIGS. 5A and 5B.

The pulsed laser beam outputted from the master oscillator MO, which maybe a diverging beam, gradually expanding its beam width, may bereflected by the high-reflective mirror 18 and then be incident on thespherical convex lens 45 of the beam-adjusting optical system 40 a.

The laser beam incident on the spherical convex lens 45 as the divergingbeam may be changed to a converging beam by the spherical convex lens45. The converging beam gradually narrowing its beam widths both in theV direction and in the H direction may enter the spherical concave lens46.

The front-side focal point F2 of the spherical concave lens 46 may belocated slightly downstream from the rear-side focal point F1 of thespherical convex lens 45 in the optical path of the laser beam. In thisconfiguration, the laser beam transmitted by the spherical concave lens46 may be a nearly parallel beam.

The laser beam transmitted by the spherical concave lens 46 may beconverted such that the beam width in the V direction is substantiallyequal to the gap distance between the second pair of dischargeelectrodes 21 a and 21 b or the beam width in the H direction issubstantially equal to the width of the discharge space of the poweramplifier PA and may enter the power amplifier PA.

The beam-adjusting optical system 40 b may adjust the beam width in theV direction to be substantially equal to the gap distance between thesecond pair of discharge electrodes 21 a and 21 b, or adjust the beamwidth in the H direction to be substantially equal to the width of thedischarge space of the power amplifier PA. Further, the beam-adjustingoptical system 40 b may set the distance between the lenses to a valuebetween a distance where the beam width in the V direction issubstantially equal to the gap distance between the second pair ofdischarge electrodes 21 a and 21 b and a distance where the beam widthin the H direction is substantially equal to the width of the dischargespace of the power amplifier PA.

According to the second example as explained above, the laser beam mayenter the power amplifier PA with the reduced beam widths both in the Vdirection and in the H direction. Therefore, wasting a part of the laserbeam may be suppressed, as compared to that in the first example.Further, pulse energy of the pulsed laser beam outputted from the poweramplifier PA may thus increase.

3.7 THIRD EXAMPLE OF BEAM-ADJUSTING OPTICAL SYSTEM

FIG. 7A shows a beam-adjusting optical system 40 c as viewed in the −Vdirection. The beam-adjusting optical system 40 c may represent a thirdexample of the beam-adjusting optical system 40 according to the firstembodiment shown in FIG. 3A. FIG. 7B shows the beam-adjusting opticalsystem 40 c as viewed in the −H direction.

The beam-adjusting optical system 40 c may include a cylindrical convexlens 41 and a cylindrical concave lens 42. Configurations and operationsof the cylindrical convex lens 41 and the cylindrical concave lens 42may be substantially the same as those in the first example describedwith reference to FIGS. 5A and 5B.

The beam-adjusting optical system 40 c may further include a cylindricalconvex lens 43 and a cylindrical concave lens 44. Both the cylindricalconvex lens 43 and the cylindrical concave lens 44 may be located in theoptical path of the laser beam. The cylindrical convex lens 43 may belocated upstream from the cylindrical concave lens 44 in the opticalpath of the laser beam.

The cylindrical convex lens 43 may have a rear-side focal axis F3located downstream from the cylindrical convex lens 43 in the opticalpath of the laser beam at a distance corresponding to a focal lengthFL3.

The cylindrical concave lens 44 may have a front-side focal axis F4located downstream from the cylindrical concave lens 44 in the opticalpath of the laser beam at a distance corresponding to a focal lengthFL4.

The rear-side focal axis F3 of the cylindrical convex lens 43 and thefront-side focal axis F4 of the cylindrical concave lens 44 may each besubstantially parallel to the V direction. The rear-side focal axis F3of the cylindrical convex lens 43 and the front-side focal axis F4 ofthe cylindrical concave lens 44 may be located in the vicinity of eachother. The front-side focal axis F4 of the cylindrical concave lens 44may be located slightly downstream from the rear-side focal axis F3 ofthe cylindrical convex lens 43 in the optical path of the laser beam.

The cylindrical convex lens 43 may be held by a holder 56. Thecylindrical concave lens 44 may be held by a holder 57. The holder 57,which holds the cylindrical concave lens 44, may be held by a uniaxialstage 58 and capable of moving along the optical path axis of the laserbeam. The holder 55 and the uniaxial stage 58 may be held by a plate 59.This may allow the cylindrical concave lens 44 to move in a directionparallel to the Z direction along the optical path axis of the laserbeam and to change distance from the cylindrical convex lens 43.

The uniaxial stage 58 may have a micrometer (not shown) to adjust thedistance between the cylindrical convex lens 43 and the cylindricalconcave lens 44 along the optical path axis of the laser beam.

In the above-described configuration, the distance between thecylindrical convex lens 41 and the cylindrical concave lens 42 may beadjusted such that the beam width in the V direction of the laser beamis substantially equal to the gap distance between the second pair ofdischarge electrodes 21 a and 21 b. Further, the distance between thecylindrical convex lens 43 and the cylindrical concave lens 44 may beadjusted such that the beam width in the H direction of the laser beamis substantially equal to the width of the discharge space of the poweramplifier PA.

According to the third example as explained above, the beam widths ofthe laser beam may be controlled separately in the V direction and inthe H direction. Therefore, wasting a part of the laser beam may furtherbe suppressed, as compared to that in the first example or in the secondexample. Further, pulse energy of the pulsed laser beam outputted fromthe power amplifier PA may thus increase.

3.8 FOURTH EXAMPLE OF BEAM-ADJUSTING OPTICAL SYSTEM

FIG. 8A shows a beam-adjusting optical system 40 d as viewed in the −Vdirection. The beam-adjusting optical system 40 d may represent a fourthexample of the beam-adjusting optical system 40 according to the firstembodiment shown in FIG. 3A. FIG. 8B shows the beam-adjusting opticalsystem 40 d as viewed in the −H direction.

In the fourth example, the two cylindrical convex lenses in the thirdexample described with reference to FIGS. 7A and 7B may be substitutedby a cylindrical biconvex lens.

The beam-adjusting optical system 40 d may include a cylindricalbiconvex lens 47, a cylindrical concave lens 42, and a cylindricalconcave lens 44. These cylindrical lenses may be provided in the opticalpath of the laser beam. The cylindrical biconvex lens 47 may be locatedupstream from the cylindrical concave lens 42 and the cylindricalconcave lens 44 in the optical path of the laser beam.

The cylindrical biconvex lens 47 may have a first cylindrical convexsurface having an axis parallel to the H direction and a secondcylindrical convex surface having an axis parallel to the V direction.The cylindrical biconvex lens 47 may have a rear-side focal axis F1located downstream from the cylindrical biconvex lens 47 in the opticalpath of the laser beam at a distance corresponding to a focal lengthFL1. Further, the cylindrical biconvex lens 47 may have a rear-sidefocal axis F3 located downstream from the cylindrical biconvex lens 47in the optical path of the laser beam at a distance corresponding to afocal length FL3.

The rear-side focal axis F1 of the cylindrical biconvex lens 47 and thefront-side focal axis F2 of the cylindrical concave lens 42 may each beparallel to the H direction. The rear-side focal axis F1 of thecylindrical biconvex lens 47 and the front-side focal axis F2 of thecylindrical concave lens 42 may be located in the vicinity of eachother. The front-side focal axis F2 of the cylindrical concave lens 42may be located slightly downstream from the rear-side focal axis F1 ofthe cylindrical biconvex lens 47 in the optical path of the laser beam.

The rear-side focal axis F3 of the cylindrical biconvex lens 47 and thefront-side focal axis F4 of the cylindrical concave lens 44 may each besubstantially parallel to the V direction. The rear-side focal axis F3of the cylindrical biconvex lens 47 and the front-side focal axis F4 ofthe cylindrical concave lens 44 may be located in the vicinity of eachother. The front-side focal axis F4 of the cylindrical concave lens 44may be located slightly downstream from the rear-side focal axis F3 ofthe cylindrical biconvex lens 47 in the optical path of the laser beam.

The cylindrical biconvex lens 47 may be held by a holder 51. Thecylindrical concave lens 42 may be held by a holder 52. The cylindricalconcave lens 44 may be held by a holder 57.

The configuration of holding the cylindrical biconvex lens 47, thecylindrical concave lens 42, and the cylindrical concave lens 44 and theconfiguration of adjusting their positions may be substantially the sameas those described with reference to FIGS. 7A and 7B.

According to the above-described configurations, the distance betweenthe cylindrical biconvex lens 47 and the cylindrical concave lens 42 maybe adjusted such that the beam width of the laser beam in the Vdirection is substantially equal to the gap distance between the secondpair of discharge electrodes 21 a and 21 b. Further, the distancebetween the cylindrical biconvex lens 47 and the cylindrical concavelens 44 may be adjusted such that the beam width of the laser beam inthe H direction is substantially equal to the width of the dischargespace of the power amplifier PA.

According to the fourth example described above, the beam widths of thelaser beam may be controlled separately in the V direction and in the Hdirection. Further, according to the fourth example, the number oflenses may be reduced as compared to that in the third example and thusthe configuration may be simplified.

3.9 FIFTH EXAMPLE OF BEAM-ADJUSTING OPTICAL SYSTEM

FIG. 9A shows a beam-adjusting optical system 40 e as viewed in the −Vdirection. The beam-adjusting optical system 40 e may represent a fifthexample of the beam-adjusting optical system 40 according to the firstembodiment shown in FIG. 3A. FIG. 9B shows the beam-adjusting opticalsystem 40 e as viewed in the −H direction.

In the fifth example, the cylindrical concave lens in the first exampledescribed with reference to FIGS. 5A and 5B may be substituted by acylindrical convex lens, which is an optical element with a positivepower.

The beam-adjusting optical system 40 e may include a cylindrical convexlens 41 and a cylindrical convex lens 48. Both the cylindrical convexlens 41 and the cylindrical convex lens 48 may be located in the opticalpath of the laser beam. The cylindrical convex lens 41 may be locatedupstream from the cylindrical convex lens 48 in the optical path of thelaser beam.

The cylindrical convex lens 41 may have a rear-side focal axis F1located downstream from the cylindrical convex lens 41 in the opticalpath of the laser beam at a distance corresponding to a focal lengthFL1.

The cylindrical convex lens 48 may have a front-side focal axis F2located upstream from the cylindrical convex lens 48 in the optical pathof the laser beam at a distance corresponding to a focal length FL2.When parallel rays of light are transmitted by the cylindrical convexlens 48 from the right side in the figure, the front-side focal axis F2of the cylindrical convex lens 48 may be an axis corresponding to a linefocus on which the rays of light are to be focused at the left side.

The focal length FL2 of the cylindrical convex lens 48 may be shorterthan the focal length FL1 of the cylindrical convex lens 41. Therear-side focal axis F1 of the cylindrical convex lens 41 and thefront-side focal axis F2 of the cylindrical convex lens 48 may each besubstantially parallel to the H direction. The rear-side focal axis F1of the cylindrical convex lens 41 and the front-side focal axis F2 ofthe cylindrical convex lens 48 may be located in the vicinity of eachother. The front-side focal axis F2 of the cylindrical convex lens 48may be located slightly downstream from the rear-side focal axis F1 ofthe cylindrical convex lens 41 in the optical path of the laser beam.

The cylindrical convex lens 41 may be held by a holder 51. Thecylindrical convex lens 48 may be held by a holder 52.

The configuration of holding the lenses and adjusting their positionsmay be substantially the same as that of the first example describedwith reference to FIGS. 5A and 5B.

The pulsed laser beam outputted from the master oscillator MO, which maybe a diverging beam gradually expanding its beam width, may be reflectedby the high-reflective mirror 18 and then be incident on the cylindricalconvex lens 41 of the beam-adjusting optical system 40 e.

The laser beam incident on the cylindrical convex lens 41 as thediverging beam may then be focused on a point located slightlydownstream from the rear-side focal axis F1 of the cylindrical convexlens 41 in the optical path of the laser beam, then diverge, and thenenter the cylindrical convex lens 48.

The front-side focal axis F2 of the cylindrical convex lens 48 may belocated slightly downstream from the rear-side focal axis F1 of thecylindrical convex lens 41 in the optical path of the laser beam. Inthis configuration, the laser beam transmitted by the cylindrical convexlens 48 may be a nearly parallel beam.

The laser beam transmitted by the cylindrical convex lens 48 may beconverted such that the beam width in the V direction is substantiallyequal to the gap distance between the second pair of dischargeelectrodes 21 a and 21 b and may enter the power amplifier PA.

As shown in FIG. 9B, let A be the beam width in the V direction of thelaser beam incident on the cylindrical convex lens 41 and let B be thebeam width in the V direction of the laser beam transmitted by thecylindrical convex lens 48. It is preferable that the following formulaeare satisfied:

B≈G, and

B/A≈FL2/FL1.

Here, G may be the gap distance between the second pair of dischargeelectrodes 21 a and 21 b. Based on the beam width A in the V directionof the laser beam incident on the cylindrical convex lens 41 and the gapdistance G between the second pair of discharge electrodes 21 a and 21b, the ratio FL2/FL1 of the focal lengths of the lenses may bedetermined and the beam width of the laser beam may be adjusted to adesirable value.

In this example, the rear-side focal axis F1 of the cylindrical convexlens 41 and the front-side focal axis F2 of the cylindrical convex lens48 may each be substantially parallel to the H direction. However, thepresent disclosure may not necessarily be limited to this example.

For another example, the rear-side focal axis F1 of the cylindricalconvex lens 41 and the front-side focal axis F2 of the cylindricalconvex lens 48 may be substantially parallel to the V direction.

Further, the spherical concave lens in the second example described withreference to FIGS. 6A and 6B may be substituted by a spherical convexlens. In this configuration, the front-side focal point F2 of thespherical convex lens, which replaces the spherical concave lens 46, maybe located slightly downstream from the rear-side focal point F1 of thespherical convex lens 45 in the optical path of the laser beam.

Further, the cylindrical concave lenses in the third example describedwith reference to FIGS. 7A and 7B may be substituted by cylindricalconvex lenses. In this configuration, the front-side focal axis F2 ofone of the cylindrical convex lenses, which replaces the cylindricalconcave lens 42, may be located slightly downstream from the rear-sidefocal axis F1 of the cylindrical convex lens 41 in the optical path ofthe laser beam. Further, the front-side focal axis F4 of another one ofthe cylindrical convex lenses, which replaces the cylindrical concavelens 44, may be located slightly downstream from the rear-side focalaxis F3 of the cylindrical convex lens 43 in the optical path of thelaser beam.

Furthermore, the cylindrical concave lenses in the fourth exampledescribed with reference to FIGS. 8A and 8B may be substituted bycylindrical convex lenses. Also in this configuration, the front-sidefocal axis F2 of one of the cylindrical convex lenses, which replacesthe cylindrical concave lens 42, may be located slightly downstream fromthe rear-side focal axis F1 of the cylindrical biconvex lens 47 in theoptical path of the laser beam. Further, the front-side focal axis F4 ofanother one of the cylindrical convex lenses, which replaces thecylindrical concave lens 44, may be located slightly downstream from therear-side focal axis F3 of the cylindrical biconvex lens 47 in theoptical path axis of the laser beam.

4. LASER DEVICE INCLUDING BOTH-SIDE TELECENTRIC BEAM-ADJUSTING OPTICALSYSTEM 4.1 CONFIGURATION

FIGS. 10A and 10B schematically show a configuration of a laser deviceaccording to a second embodiment of the present disclosure. The laserdevice of the second embodiment may include a beam-adjusting opticalsystem 60 a that is a both-side telecentric optical system. Thebeam-adjusting optical system 60 a may be provided in the beam path ofthe laser beam between the high-reflective mirrors 18 and 19.

The beam-adjusting optical system 60 a may include a spherical convexlens 61 and a spherical convex lens 62 each having a focal length FL1.Both the spherical convex lens 61 and the spherical convex lens 62 maybe provided in the optical path of the laser beam.

The spherical convex lens 61 and the spherical convex lens 62 may bearranged such that the rear-side focal point of the spherical convexlens 61 and the front-side focal point of the spherical convex lens 62substantially coincide with each other. Here, a hypothetical aperturemay be disposed at a position where these focal points coincide witheach other. Rays of light passing the center of the hypotheticalaperture may be substantially parallel to the optical path axis of thelaser beam in the optical path upstream from the spherical convex lens61. Namely, an entrance pupil of the beam-adjusting optical system 60 amay be located at infinity. Further, rays of light passing the center ofthe hypothetical aperture may be made substantially parallel to theoptical path axis of the laser beam in the optical path downstream fromthe spherical convex lens 62. Namely, an exit pupil of thebeam-adjusting optical system 60 a may be located at infinity.

In addition, the partially-reflective surface of the output couplingmirror 15 may be positioned at the front-side focal point of thespherical convex lens 61. In FIG. 10A, a sum of the distance FL1 a fromthe spherical convex lens 61 to the high-reflective mirror 18 and thedistance FL1 b from the high-reflective mirror 18 to thepartially-reflective surface of the output coupling mirror 15 may begiven by the following formula:

FL1a+FL1b=FL1.

Similarly, a sum of the distance FL1 a′ from the spherical convex lens62 to the high-reflective mirror 19 and the distance FL1 b′ from thehigh-reflective mirror 19 to the rear-side focal point of the sphericalconvex lens 62 may also be FL1. In this configuration, an image of thepartially-reflective surface of the output coupling mirror 15 may beformed at a position of the rear-side focal plane of the sphericalconvex lens 62 at a substantially equal magnification. Namely, an objectplane O shown in FIG. 10A may be transferred at a magnification of 1:1to an image plane I shown in FIG. 10A.

4.2 OPERATION

FIG. 11A shows a beam profile in a cross section of the laser beam atline XIA in FIG. 10A. FIG. 11B shows a beam profile in a cross sectionof the laser beam at line XIB in FIG. 10A. FIG. 11C shows a beam profilein a cross section of the laser beam at line XIC in FIG. 10A.

The laser beam outputted from the master oscillator MO may be reflectedby the high-reflective mirrors 18 and 19, then pass the beam-adjustingoptical system 60 a, and then enter the power amplifier PA. Thebeam-adjusting optical system 60 a may transfer the object plane Olocated at the partially-reflective surface of the output couplingmirror 15 of the master oscillator MO at a magnification of 1:1 to theimage plane I located downstream from the beam-adjusting optical system60 a in the optical path of the laser beam. Therefore, the beam profileof the cross section of the beam shown in FIG. 11A and the beam profileof the cross section of the beam shown in FIG. 11B may be substantiallyequal to each other.

Further, the beam-adjusting optical system 60 a may be a both-sidetelecentric optical system. According to this configuration, moving theobject plane O along the optical path axis of the laser beam causeslittle change in the magnification. Further, moving the image plane Ialong the optical path axis of the laser beam also causes little changein the magnification.

4.3 EFFECT

According to the above-described configuration, the problem where a partof the laser beam does not enter the discharge space of the poweramplifier PA to be wasted may be suppressed. The pulse energy of thepulsed laser beam outputted from the power amplifier PA may thusincrease.

4.4 OTHERS

The present embodiment shows an example where the beam-adjusting opticalsystem 60 a is provided in the optical path between the high-reflectivemirrors 18 and 19. However, the present disclosure may not necessarilybe limited to this example. The beam-adjusting optical system 60 a maybe provided at any position in the optical path between the outputcoupling mirror 15 and the window 20 a.

Further, explanation was made for an example where the focal length ofthe spherical convex lens 61 and the focal length of the sphericalconvex lens 62 may be substantially equal to each other. However, thepresent disclosure may not necessarily be limited to this example. Thespherical convex lens 61 and the spherical convex lens 62 may havedifferent focal lengths from each other according to a ratio of the gapdistance between the first pair of discharge electrodes 11 a and 11 b tothe gap distance between the second pair of discharge electrodes 21 aand 21 b.

Further, explanation was made for an example where the object plane Omay be located in the partially-reflective surface of the outputcoupling mirror 15 and the image plane I may be located in the vicinityof the window 20 a of the power amplifier PA. However, the presentdisclosure may not necessarily be limited to this example. The objectplane O may be located in the optical resonator of the master oscillatorMO. The object plane O may be located between the window 10 a and thewindow 10 b of the master oscillator MO. The image plane I may belocated between the window 20 a and the window 20 b of the poweramplifier PA. Preferably, the object plane O may be located between thefirst pair of discharge electrodes 11 a and 11 b and the image plane Imay be located between the second pair of discharge electrodes 21 a and21 b. More preferably, the object plane O may be located substantiallyat the center of the discharge space between the first pair of dischargeelectrodes 11 a and 11 b and the image plane I may be locatedsubstantially at the center of the discharge space between the secondpair of discharge electrodes 21 a and 21 b.

4.5 MODIFIED EXAMPLE OF SECOND EMBODIMENT

FIGS. 12A and 12B schematically show a configuration of a laser deviceof a modified example according to the second embodiment of the presentdisclosure. In this laser device, a beam-adjusting optical system 60 bthat is a both-side telecentric optical system may be configured byusing two off-axis paraboloidal mirrors 68 and 69.

Both the off-axis paraboloidal mirror 68 and the off-axis paraboloidalmirror 69 may be located in the optical path of the laser beam. Theoff-axis paraboloidal mirror 68 may be located upstream from theoff-axis paraboloidal mirror 69 in the optical path of the laser beam.

The off-axis paraboloidal mirror 68 and the off-axis paraboloidal mirror69 may each be a mirror in which an inner surface of paraboloid ofrevolution is used for a reflective surface. The off-axis paraboloidalmirror 68 and the off-axis paraboloidal mirror 69 may be arranged suchthat the axes of the respective paraboloids of revolution aresubstantially parallel to each other and that the respective focalpoints F1 are substantially coincide with each other.

Parallel rays of the laser beam from the master oscillator MO may beincident on the off-axis paraboloidal mirror 66 in a direction parallelto the axis of the paraboloid of revolution. In this case, the off-axisparaboloidal mirror 68 may change the optical path axis of the laserbeam by 90 degrees and focus the laser beam on a focal point F1.

A laser beam diverged from the focal point F1 may be incident on theoff-axis paraboloidal mirror 69. In this case, the off-axis paraboloidalmirror 69 may change the optical path axis of the laser beam by 90degrees and reflect the laser beam with parallel rays to the poweramplifier PA in a direction parallel to the axis of the paraboloid ofrevolution. Practically, the laser beam may not necessarily include theparallel rays but may have some angle of divergence.

The focal lengths of the off-axis paraboloidal mirror 68 and theoff-axis paraboloidal mirror 69 may be substantially equal to eachother. In this configuration, an object plane O located upstream fromthe off-axis paraboloidal mirror 68 in the optical path of the laserbeam at a distance corresponding to a focal length FL1 may betransferred at a magnification of 1:1 to an image plane I locateddownstream from the off-axis paraboloidal mirror 69 in the optical pathof the laser beam at a distance corresponding to the focal length FL1.The object plane O may be located in the discharge space of the masteroscillator MO. The image plane I may be located in the discharge spaceof the power amplifier PA.

This modified example may have substantially the same effect as that ofthe beam-adjusting optical system 60 a described with reference to FIGS.10A and 10B. Further, the beam-adjusting optical system 60 b may haveboth functions of the high-reflective mirrors 18 and 19 and thebeam-adjusting optical system 60 a. Therefore, the number of opticalelements may be reduced.

The off-axis paraboloidal mirror 68 and the off-axis paraboloidal mirror69 may have different focal lengths from each other according to a ratioof the dimension of the discharge space of the master oscillator MO andthe dimension of the discharge space of the power amplifier PA.

5. LASER DEVICE INCLUDING PLURALITY OF POWER AMPLIFIERS 5.1CONFIGURATION

FIG. 13 schematically shows a configuration of a laser device accordingto a third embodiment of the present disclosure. The laser device of thethird embodiment may include a first amplifier PA1 and a secondamplifier PA2 as well as the master oscillator MO.

The configurations of the master oscillator MO and the first amplifierPA1 may be the same as the respective configurations of the masteroscillator MO and the power amplifier PA described above. The secondamplifier PA2 may include a third laser chamber 30 and a third pair ofdischarge electrodes 31 a and 31 b. The third pair of dischargeelectrodes 31 a and 31 b may be provided in the third laser chamber 30.The third laser chamber 30 may have windows 30 a and 30 b at respectiveends of the third laser chamber 30. Specific configurations of thesecond amplifier PA2 may be substantially the same as those of the firstamplifier PA1.

In the optical path of the laser beam between the master oscillator MOand the first amplifier PA1, optical elements such as thehigh-reflective mirrors 18 and 19, and in addition, a convex lens 61 anda convex lens 62 constituting a both-side telecentric beam-adjustingoptical system may be disposed. The convex lens 61 and the convex lens62 may each have a focal length FL1. In FIG. 13, sum of the distance FL1a from the convex lens 61 to the high-reflective mirror 18 and thedistance FL1 b from the high-reflective mirror 18 to the rear-side focalpoint of the convex lens 61 may be expressed by the following formula:

FL1a+FL1b=FL1.

Similarly, sum of the distance FL1 b′ from the front-side focal point ofthe convex lens 62 to the high-reflective mirror 19 and the distance FL1a′ from the high-reflective mirror 1 to the convex lens 62 may also beFL1.

In the optical path of the laser beam between the first amplifier PA1and the second amplifier PA2, optical elements such as high-reflectivemirrors 28 and 29, and in addition, a convex lens 63 and a convex lens64 constituting a both-side telecentric beam-adjusting optical systemmay be disposed. The convex lens 63 and the convex lens 64 may each havea focal length FL2. In FIG. 13, sum of the distance FL2 a from theconvex lens 63 to the high-reflective mirror 28 and the distance FL2 bfrom the high-reflective mirror 28 to the rear-side focal point of theconvex lens 63 may be represented by the following formula:

FL2a+FL2b=FL2.

Similarly, sum of the distance FL2 b′ from the front-side focal point ofthe convex lens 64 to the high-reflective mirror 29 and the distance FL2a′ from the high-reflective mirror 29 to the convex lens 64 may also beFL2.

The focal length FL1 of each of the convex lens 61 and the convex lens62 may be different from the focal length FL2 of each of the convex lens63 and the convex lens 64.

5.2 OPERATION AND EFFECT

FIG. 14A schematically shows an optical arrangement of the laser deviceshown in FIG. 13.

The front-side focal point of the convex lens 61 may be locatedsubstantially at the center of the discharge space of the masteroscillator MO. The rear-side focal point of the convex lens 62 may belocated substantially at the center of the discharge space of the firstamplifier PA1. According to this configuration, an object plane Olocated substantially at the center of the discharge space of the masteroscillator MO may be transferred to a first image plane I1 locatedsubstantially at the center of the discharge space of the firstamplifier PA1.

The front-side focal point of the convex lens 63 may be locatedsubstantially at the center of the discharge space of the firstamplifier PA1. The rear-side focal point of the convex lens 64 may belocated substantially at the center of the discharge space of the secondamplifier PA2. According to this configuration, the first image plane I1located substantially at the center of the discharge space of the firstamplifier PA1 may be transferred to a second image plane 12 of thedischarge space of the second amplifier PA2.

As explained above, the rear-side focal point of the convex lens 62 andthe front-side focal point of the convex lens 63 may substantiallycoincide with each other. In this case, the object plane O locatedsubstantially at the center of the discharge space of the masteroscillator MO may be transferred to the second image plane 12 locatedsubstantially at the center of the discharge space of the secondamplifier PA2.

According to the above-described configuration, a part of the laser beamto be wasted may be reduced, the pulse energy of the pulsed laser beamoutputted from the second amplifier PA2 may increase, and alignment ofthe optical paths from the master oscillator MO to the second amplifierPA2 may be improved.

5.3 MODIFIED EXAMPLES OF THIRD EMBODIMENT

FIG. 14B schematically shows an optical arrangement of a laser device ofa first modified example according to the third embodiment of thepresent disclosure. In this laser device, a beam-adjusting opticalsystem constituted by a convex lens 61 and a convex lens 62 may beboth-side telecentric. The beam-adjusting optical system may have afirst object plane O1 at a first end, which is close to the outputcoupling mirror, of the discharge space of the master oscillator MO. Thebeam-adjusting optical system may have a first image plane I1 at a firstend, which is close to an entrance, of the discharge space of the firstamplifier PA1. Further, a beam-adjusting optical system constituted by aconvex lens 63 and a convex lens 64 may be both-side telecentric. Thebeam-adjusting optical system may have a second object plane O2 at asecond end, which is close to an exit, of the discharge space of thefirst amplifier PA1. The beam-adjusting optical system may have a secondimage plane 12 at a first end, which is close to an entrance, of thedischarge space of the second amplifier PA2.

FIG. 14C schematically shows an optical arrangement of a laser device ofa second modified example according to the third embodiment of thepresent disclosure. In this laser device, a beam-adjusting opticalsystem constituted by a convex lens 41 a and a concave lens 42 a may beprovided between the master oscillator MO and the first amplifier PA1.Further, a beam-adjusting optical system constituted by a convex lens 41b and a concave lens 42 b may be provided between the first amplifierPA1 and the second amplifier PA2.

The aforementioned descriptions are intended to be taken only asexamples and are not to be seen as limiting in any way. Accordingly, itwill be clear to those skilled in the art that variations on theembodiments of the present disclosure may be made without departing fromthe scope of the appended claims.

The terms used in the present specification and in the entirety of thescope of the appended claims are to be interpreted as not beinglimiting. For example, wording such as “includes” or “is included”should be interpreted as not being limited to the item that is describedas being included. Furthermore, “has” should be interpreted as not beinglimited to the item that is described as being had. Furthermore, themodifier “a” or “an” as used in the present specification and the scopeof the appended claims should be interpreted as meaning “at least one”or “one or more”.

1. A laser device comprising: a master oscillator including a first laser chamber, a first pair of discharge electrodes provided in the first laser chamber, and an optical resonator, the master oscillator being configured to output a laser beam; a first amplifier including a second laser chamber provided in an optical path of the laser beam outputted from the master oscillator and a second pair of discharge electrodes provided in the second laser chamber at a first gap distance, the first amplifier being configured to amplify the laser beam; and a first beam-adjusting optical system provided in an optical path of the laser beam between the master oscillator and the first amplifier, the first beam-adjusting optical system being configured to adjust the laser beam outputted from the master oscillator such that a beam width of the laser beam entering the first amplifier measured in a direction of electric discharge between the second pair of discharge electrodes is substantially equal to the first gap distance between the second pair of discharge electrodes.
 2. The laser device according to claim 1, wherein the first beam-adjusting optical system includes a first optical element with a positive power and a second optical element with a positive or negative power provided downstream from the first optical element in the optical path of the laser beam.
 3. The laser device according to claim 2, wherein the first optical element has a first focal length FL1, the second optical element has a second focal length FL2 equal to or less than the first focal length FL1, and a ratio B/A is expressed by a formula B/A≈FL2/FL1, where A represents a first beam width of the laser beam entering the first optical element, B represents a second beam width of the laser beam emitting from the second optical element, the first beam width A and the second beam width B are both in the direction of electric discharge between the second pair of discharge electrodes, and the second beam width B is substantially equal to the first gap distance between the second pair of discharge electrodes.
 4. A laser device comprising: a master oscillator including a first laser chamber, a first pair of discharge electrodes provided in the first laser chamber, and an optical resonator, the master oscillator being configured to output a laser beam; a first amplifier including a second laser chamber provided in an optical path of the laser beam outputted from the master oscillator and a second pair of discharge electrodes provided in the second laser chamber, the first amplifier being configured to amplify the laser beam; and a first beam-adjusting optical system provided in an optical path of the laser beam between the master oscillator and the first amplifier, the first beam-adjusting optical system being configured to adjust the laser beam outputted from the master oscillator, the first beam-adjusting optical system including a first optical element with a positive power and a second optical element with a positive or negative power provided downstream from the first optical element in the optical path of the laser beam.
 5. The laser device according to claim 4, wherein the first optical element has a first focal length FL1, the second optical element has a second focal length FL2 equal to or less than the first focal length FL1, and a front-side focal point of the second optical element is located slightly downstream from a rear-side focal point of the first optical element in the optical path of the laser beam.
 6. A laser device comprising: a master oscillator including a first laser chamber, a first pair of discharge electrodes provided in the first laser chamber, and an optical resonator, the master oscillator being configured to output a laser beam; a first amplifier including a second laser chamber provided in an optical path of the laser beam outputted from the master oscillator and a second pair of discharge electrodes provided in the second laser chamber, the first amplifier being configured to amplify the laser beam; and a first beam-adjusting optical system provided in an optical path of the laser beam between the master oscillator and the first amplifier, the first beam-adjusting optical system being a both-side telecentric optical system.
 7. The laser device according to claim 6, wherein the first beam-adjusting optical system has a substantially equal magnification.
 8. The laser device according to claim 6, wherein an object point of the first beam-adjusting optical system is located in the optical resonator, and an image point of the first beam-adjusting optical system is located between the second pair of discharge electrodes.
 9. The laser device according to claim 6, wherein an object point of the first beam-adjusting optical system is located substantially at a center of the optical resonator, and an image point of the first beam-adjusting optical system is located substantially at a center of a space between the second pair of discharge electrodes.
 10. The laser device according to claim 1, further comprising: a second amplifier including a third laser chamber provided in an optical path of the, laser beam outputted from the first amplifier and a third pair of discharge electrodes provided in the third laser chamber at a second gap distance, the second amplifier being configured to amplify the laser beam outputted from the first amplifier; and a second beam-adjusting optical system provided in an optical path of the laser beam between the first amplifier and the second amplifier, the second beam-adjusting optical system being configured to adjust the laser beam outputted from the first amplifier such that a beam width of the laser beam entering the second amplifier measured in a direction of electric discharge between the third pair of discharge electrodes is substantially equal to the second gap distance between the third pair of discharge electrodes.
 11. The laser device according to claim 4, further comprising: a second amplifier including a third laser chamber provided in an optical path of the laser beam outputted from the first amplifier and a third pair of discharge electrodes provided in the third laser chamber, the second amplifier being configured to amplify the laser beam outputted from the first amplifier; and a second beam-adjusting optical system provided in an optical path of the laser beam between the first amplifier and the second amplifier, the second beam-adjusting optical system being configured to adjust the laser beam outputted from the first amplifier, the second beam-adjusting optical system including a third optical element with a positive power and a fourth optical element with a positive or negative power provided downstream from the third optical element in the optical path of the laser beam.
 12. The laser device according to claim 6, further comprising: a second amplifier including a third laser chamber provided in an optical path of the laser beam outputted from the first amplifier and a third pair of discharge electrodes provided in the third laser chamber, the second amplifier being configured to amplify the laser beam outputted from the first amplifier; and a second beam-adjusting optical system provided in an optical path of the laser beam between the first amplifier and the second amplifier, the second beam-adjusting optical system being a both-side telecentric optical system.
 13. The laser device according to claim 12, wherein an object point of the first beam-adjusting optical system is located substantially at a center of the optical resonator, an image point of the first beam-adjusting optical system and an object point of the second beam-adjusting optical system are both located substantially at a center of a space between the second pair of discharge electrodes, and an image point of the second beam-adjusting optical system is located substantially at a center of a space between the third pair of discharge electrodes.
 14. The laser device according to claim 1, wherein the first pair of discharge electrodes is provided in the first laser chamber at the first gap distance. 